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      <h1>OpenWrt Buildroot</h1>
    </div>

    <p>Usage and documentation by Felix Fietkau and Waldemar Brodkorb, based on uClibc Buildroot
    documentation by Thomas Petazzoni. Contributions from Karsten Kruse,
    Ned Ludd, Martin Herren. OpenWrt Kernel Module Creation Howto by Markus Becker.</p>

    <p><small>Last modification : $Id: buildroot-documentation.html 3602 2006-04-08 21:21:01Z mbm $</small></p>

    <ul>
      <li><a href="#about">About OpenWrt Buildroot</a></li>
      <li><a href="#download">Obtaining OpenWrt Buildroot</a></li>
      <li><a href="#using">Using OpenWrt Buildroot</a></li>
      <li><a href="#custom_targetfs">Customizing the target filesystem</a></li>
      <li><a href="#custom_busybox">Customizing the Busybox
      configuration</a></li>
      <li><a href="#custom_uclibc">Customizing the uClibc
      configuration</a></li>
      <li><a href="#buildroot_innards">How OpenWrt Buildroot works</a></li>
      <li><a href="#using_toolchain">Using the uClibc toolchain</a></li>
      <li><a href="#toolchain_standalone">Using the uClibc toolchain
      outside of Buildroot</a></li>
      <li><a href="#downloaded_packages">Location of downloaded packages</a></li>
      <li><a href="#add_software">Extending OpenWrt with more Software</a></li>
      <li><a href="#links">Ressources</a></li>
<br>
      <li><a href="#about_module">About OpenWrt Kernel Module Compilation</a></li>
      <li><a href="#kernel">Enable the kernel options</a></li>
      <li><a href="#buildroot_option">Create a buildroot option</a></li>
      <li><a href="#binary">Define the binary files for the kernel module</a></li>
      <li><a href="#control">Specify the ipkg control file</a></li>
      <li><a href="#compile">Compile the kernel module</a></li>
 
    </ul>

    <h2><a name="about" id="about"></a>About OpenWrt Buildroot</h2>

    <p>OpenWrt Buildroot is a set of Makefiles and patches that allows to easily
    generate both a cross-compilation toolchain and a root filesystem for your
    Wireless Router. The cross-compilation toolchain uses uClibc (<a href=
    "http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard
    library.</p>

    <p>A compilation toolchain is the set of tools that allows to
    compile code for your system. It consists of a compiler (in our
    case, <code>gcc</code>), binary utils like assembler and linker
    (in our case, <code>binutils</code>) and a C standard library (for
    example <a href="http://www.gnu.org/software/libc/libc.html">GNU
    Libc</a>, <a href="http://www.uclibc.org">uClibc</a> or <a
    href="http://www.fefe.de/dietlibc/">dietlibc</a>). The system
    installed on your development station certainly already has a
    compilation toolchain that you can use to compile application that
    runs on your system. If you're using a PC, your compilation
    toolchain runs on an x86 processor and generates code for a x86
    processor. Under most Linux systems, the compilation toolchain
    uses the GNU libc as C standard library.  This compilation
    toolchain is called the "host compilation toolchain", and more
    generally, the machine on which it is running, and on which you're
    working is called the "host system". The compilation toolchain is
    provided by your distribution, and OpenWrt Buildroot has nothing to do
    with it.</p>

    <p>As said above, the compilation toolchain that comes with your system
    runs and generates code for the processor of your host system. As your
    embedded system has a different processor, you need a cross-compilation
    toolchain: it's a compilation toolchain that runs on your host system but
    that generates code for your target system (and target processor). For
    example, if your host system uses x86 and your target system uses MIPS, the
    regular compilation toolchain of your host runs on x86 and generates code
    for x86, while the cross-compilation toolchain runs on x86 and generates
    code for MIPS.</p>

    <p>You might wonder why such a tool is needed when you can compile
    <code>gcc</code>, <code>binutils</code>, uClibc and all the tools by hand.
    Of course, doing so is possible. But dealing with all configure options,
    with all problems of every <code>gcc</code> or <code>binutils</code>
    version is very time-consuming and uninteresting. OpenWrt Buildroot automates this
    process through the use of Makefiles, and has a collection of patches for
    each <code>gcc</code> and <code>binutils</code> version to make them work
    on the MIPS architecture of most Wireless Routers.</p>

    <h2><a name="download" id="download"></a>Obtaining OpenWrt Buildroot</h2>

    <p>OpenWrt Buildroot is available via SVN aka subversion.
    For any kind of OpenWrt development you should get the latest version from svn via:</p>
<pre>
 $ svn co https://svn.openwrt.org/openwrt/trunk/
</pre>
    <p>If you only like to create your own custom firmware images and packages we
     strongly suggest to use the SVN branch of the stable version (whiterussian):
    </p>
<pre>
 $ svn co https://svn.openwrt.org/openwrt/branches/whiterussian/
</pre>
 

    <h2><a name="using" id="using"></a>Using OpenWrt Buildroot</h2>

    <p>OpenWrt Buildroot has a nice configuration tool similar to the one you can find
    in the Linux Kernel (<a href="http://www.kernel.org/">http://www.kernel.org/</a>)
    or in Busybox (<a href="http://www.busybox.org/">http://www.busybox.org/</a>).
    Note that you can run everything as a normal user. There is no need to be root to
    configure and use the Buildroot. The first step is to run the configuration
    assistant:</p>

<pre>
 $ make menuconfig
</pre>

    <p>For each entry of the configuration tool, you can find associated help
    that describes the purpose of the entry.</p>

    <p>Once everything is configured, the configuration tool has generated a
    <code>.config</code> file that contains the description of your
    configuration. It will be used by the Makefiles to do what's needed.</p>

    <p>Let's go:</p>

<pre>
 $ make
</pre>

    <p>This command will download, configure and compile all the selected
    tools, and finally generate target firmware images and additional packages
    (depending on your selections in <code>make menuconfig</code>.
    All the target files can be found in the <code>bin/</code> subdirectory.
    You can compile firmware images containing two different filesystem types:
    <ul>
        <li>jffs2</li>
        <li>squashfs</li>
    </ul>
    <p><code>jffs2</code> contains a writable root filesystem, which will expand to
    the size of your flash image. Note: if you use the generic firmware image, you 
    need to pick the right image for your flash size, because of different
    eraseblock sizes.</p>
    
    <p><code>squashfs</code> contains a read-only root filesystem using a modified 
    <code>squashfs</code> filesystem with LZMA compression. When booting it, you can
    create a writable second filesystem, which will contain your modifications to
    the root filesystem, including the packages you install.
    
    <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
    target filesystem</h2>

    <p>There are two ways to customize the resulting target filesystem:</p>

    <ul>
      <li>Customize the target filesystem directly, and rebuild the image. The
      target filesystem is available under <code>build_ARCH/root/</code> where
      <code>ARCH</code> is the chosen target architecture, usually mipsel.
      You can simply make your changes here, and run make target_install afterwards, 
      which will rebuild the target filesystem image. This method allows to do
      everything on the target filesystem, but if you decide to rebuild your toolchain,
      tools or packages, these changes will be lost.</li>

      <li>Customize the target filesystem skeleton, available under
      <code>package/base-files/default/</code>. You can customize
      configuration files or other stuff here. However, the full file hierarchy
      is not yet present, because it's created during the compilation process.
      So you can't do everything on this target filesystem skeleton, but
      changes to it remains even when you completely rebuild the cross-compilation
      toolchain and the tools.<br />
    </ul>

    <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
    Busybox configuration</h2>

    <p>Busybox is very configurable, and you may want to customize it.
    Its configuration is completely integrated into the main menuconfig system.
    You can find it under "OpenWrt Package Selection" =&gt; "Busybox Configuration"</p>

    <h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
    configuration</h2>

    <p>Just like <a href="#custom_busybox">BusyBox</a>, <a
    href="http://www.uclibc.org">uClibc</a> offers a lot of
    configuration options. They allow to select various
    functionalities, depending on your needs and limitations.</p>

    <p>The easiest way to modify the configuration of uClibc is to
    follow these steps :</p>

    <ol>

      <li>Make a first compilation of buildroot without trying to
      customize uClibc.</li>

      <li>Go into the directory
      <code>toolchain_build_ARCH/uClibc/</code> and run <code>make
      menuconfig</code>. The nice configuration assistant, similar to
      the one used in the Linux Kernel appears. Make
      your configuration as appropriate.</li>

      <li>Copy the <code>.config</code> file to
      <code>toolchain/uClibc/uClibc.config</code> or
      <code>toolchain/uClibc/uClibc.config-locale</code>. The former
      is used if you haven't selected locale support in the Buildroot
      configuration, and the latter is used if you have selected
      locale support.</li>

      <li>Run the compilation again.</li>

    </ol>

    <p>Otherwise, you can simply change
    <code>toolchain/uClibc/uClibc.config</code> or
    <code>toolchain/uClibc/uClibc.config-locale</code> without running
    the configuration assistant.</p>

    <h2><a name="buildroot_innards" id="buildroot_innards"></a>How OpenWrt Buildroot
    works</h2>

    <p>As said above, OpenWrt is basically a set of Makefiles that download,
    configure and compiles software with the correct options. It also includes
    some patches for various software, mainly the ones involved in the
    cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
    uClibc).</p>

    <p>There is basically one Makefile per software, and they are named <code>Makefile</code>.
    Makefiles are split into three sections:</p>

    <ul>
      <li><b>package</b> (in the <code>package/</code> directory) contains the
      Makefiles and associated files for all user-space tools that Buildroot
      can compile and add to the target root filesystem. There is one
      sub-directory per tool.</li>

      <li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
      the Makefiles and associated files for all software related to the
      cross-compilation toolchain : <code>binutils</code>, <code>ccache</code>,
      <code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
      <code>uClibc</code>.</li>

      <li><b>target</b> (in the <code>target</code> directory) contains the
      Makefiles and associated files for software related to the generation of
      the target root filesystem image and the linux kernel for the different 
      system on a chip boards, used in the Wireless Routers. 
      Two types of filesystems are supported
      : jffs2 and squashfs. 
    </ul>

    <p>Each directory contains at least 2 files :</p>

    <ul>
      <li><code>Makefile</code> is the Makefile that downloads, configures,
      compiles and installs the software <code>something</code>.</li>

      <li><code>Config.in</code> is a part of the configuration tool
      description file. It describes the option related to the current
      software.</li>
    </ul>

    <p>The main Makefile do the job through the following steps (once the
    configuration is done):</p>

    <ol>
      <li>Create the download directory (<code>dl/</code> by default). This is
      where the tarballs will be downloaded. It is interesting to know that the
      tarballs are in this directory because it may be useful to save them
      somewhere to avoid further downloads.</li>

      <li>Create the build directory (<code>build_ARCH/</code> by default,
      where <code>ARCH</code> is your architecture). This is where all
      user-space tools while be compiled.</li>

      <li>Create the toolchain build directory
      (<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code>
      is your architecture). This is where the cross compilation toolchain will
      be compiled.</li>

      <li>Setup the staging directory (<code>staging_dir_ARCH/</code> by
      default). This is where the cross-compilation toolchain will be
      installed. If you want to use the same cross-compilation toolchain for
      other purposes, such as compiling third-party applications, you can add
      <code>staging_dir_ARCH/bin</code> to your PATH, and then use
      <code>arch-linux-gcc</code> to compile your application. In order to
      setup this staging directory, it first removes it, and then it creates
      various subdirectories and symlinks inside it.</li>

      <li>Create the target directory (<code>build_ARCH/root/</code> by
      default) and the target filesystem skeleton. This directory will contain
      the final root filesystem. To set it up, it first deletes it, then it
      copies the skeleton available in  <code>target/default/target_skeleton</code>
      and then removes useless <code>SVN/</code> directories.</li>

      <li>Call the <code>prepare</code>, <code>compile</code> and <code>install</code>
      targets for the subdirectories <code>toolchain</code>, <code>package</code>
      and <code>target</code></li>
    </ol>

    <h2><a name="using_toolchain" id="using_toolchain"></a>Using the
    uClibc toolchain</h2>

    <p>You may want to compile your own programs or other software
    that are not packaged in OpenWrt. In order to do this, you can
    use the toolchain that was generated by the Buildroot.</p>

    <p>The toolchain generated by the Buildroot by default is located in
    <code>staging_dir_ARCH</code>. The simplest way to use it
    is to add <code>staging_dir_ARCH/bin/</code> to your PATH
    environment variable, and then to use
    <code>arch-linux-gcc</code>, <code>arch-linux-objdump</code>,
    <code>arch-linux-ld</code>, etc.</p>

    <p>For example, you may add the following to your
    <code>.bashrc</code> (considering you're building for the MIPS
    architecture and that Buildroot is located in
    <code>~/openwrt/</code>) :</p>

<pre>
export PATH=$PATH:~/openwrt/staging_dir_mipsel/bin/
</pre>

    <p>Then you can simply do :</p>

<pre>
mipsel-linux-uclibc-gcc -o foo foo.c
</pre>

    <p><b>Important</b> : do not try to move the toolchain to an other
    directory, it won't work. There are some hard-coded paths in the
    <i>gcc</i> configuration. If the default toolchain directory
    doesn't suit your needs, please refer to the <a
    href="#toolchain_standalone">Using the uClibc toolchain outside of
    buildroot</a> section.</p>

    <h2><a name="toolchain_standalone" id="toolchain_standalone"></a>Using the
    uClibc toolchain outside of buildroot</h2>

    <p>By default, the cross-compilation toolchain is generated inside
    <code>staging_dir_ARCH/</code>. But sometimes, it may be useful to
    install it somewhere else, so that it can be used to compile other programs
    or by other users. Moving the <code>staging_dir_ARCH/</code>
    directory elsewhere is <b>not possible</b>, because they are some hardcoded
    paths in the toolchain configuration.</p>

    <p>If you want to use the generated toolchain for other purposes,
    you can configure Buildroot to generate it elsewhere using the
    option of the configuration tool : <code>Build options -&gt;
    Toolchain and header file location</code>, which defaults to
    <code>staging_dir_ARCH/</code>.</p>

    <h2><a name="downloaded_packages"
    id="downloaded_packages"></a>Location of downloaded packages</h2>

    <p>It might be useful to know that the various tarballs that are
    downloaded by the <i>Makefiles</i> are all stored in the
    <code>DL_DIR</code> which by default is the <code>dl</code>
    directory. It's useful for example if you want to keep a complete
    version of Buildroot which is known to be working with the
    associated tarballs. This will allow you to regenerate the
    toolchain and the target filesystem with exactly the same
    versions.</p>

    <h2><a name="add_software" id="add_software"></a>Extending OpenWrt with
    more software</h2>

    <p>This section will only consider the case in which you want to
    add user-space software.</p>

    <h3>Package directory</h3>

    <p>First of all, create a directory under the <code>package</code>
    directory for your software, for example <code>foo</code>.</p>

    <h3><code>Config.in</code> file</h3>

    <p>Then, create a file named <code>Config.in</code>. This file
    will contain the portion of options description related to our
    <code>foo</code> software that will be used and displayed in the
    configuration tool. It should basically contain :</p>

<pre>
config BR2_PACKAGE_FOO
        tristate "foo - some nice tool"
        default m if CONFIG_DEVEL
        help
	     This is a comment that explains what foo is.
</pre>

    <p>If you depend on other software or library inside the Buildroot, it
    is important that you automatically select these packages in your 
    <code>Config.in</code>. Example if foo depends on bar library:
    </p>
<pre>
config BR2_PACKAGE_FOO
        tristate "foo - some nice tool"
        default m if CONFIG_DEVEL
	select BR2_PACKAGE_LIBBAR
        help
        This is a comment that explains what foo is.
</pre>

    <p>Of course, you can add other options to configure particular
    things in your software.</p>

    <h3><code>Config.in</code> in the package directory</h3>
	
    <p>To add your package to the configuration tool, you need
    to add the following line to <code>package/Config.in</code>,
    please add it to a section, which fits the purpose of foo:

<pre>
comment "Networking"
source "package/foo/Config.in"
</pre>

    <h3><code>Makefile</code> in the package directory</h3>

    <p>To add your package to the build process, you need to edit
    the Makefile in the <code>package/</code> directory. Locate the
    lines that look like the following:</p>

<pre>
package-$(BR2_PACKAGE_FOO) += foo
</pre>

   <p>As you can see, this short line simply adds the target 
   <code>foo</code> to the list of targets handled by OpenWrt Buildroot.</p>

   <p>In addition to the default dependencies, you make your package
   depend on another package (e.g. a library) by adding a line:
    
<pre>
foo-compile: bar-compile
</pre>

   <h3>The ipkg control file</h3>
   <p>Additionally, you need to create a control file which contains
   information about your package, readable by the <i>ipkg</i> package
   utility. It should be created as file:
   <code>package/foo/ipkg/foo.control</code></p>
   
   <p>The file looks like this</p>

<pre>
     1  Package: foo
     2  Priority: optional
     3  Section: net
     4  Maintainer: Foo Software &lt;foo@foosoftware.com&gt;
     5  Source: http://foosoftware.com
     6  Depends: libbar
     7  Description: Package Description
</pre>
   
   <p>You can skip the usual <code>Version:</code> and <code>Architecture</code>
   fields, as they will be generated by the <code>make-ipkg-dir.sh</code> script
   called from your Makefile. The Depends field is important, so that ipkg will
   automatically fetch all dependend software on your target system.</p>

   <h3>The real <i>Makefile</i></h3>

   <p>Finally, here's the hardest part. Create a file named
   <code>Makefile</code>. It will contain the <i>Makefile</i> rules that
   are in charge of downloading, configuring, compiling and installing
   the software. Below is an example that we will comment afterwards.</p>

<pre>
     1  # $Id: buildroot-documentation.html 3602 2006-04-08 21:21:01Z mbm $
     2	
     3  include $(TOPDIR)/rules.mk
     4
     5  PKG_NAME:=foo
     6  PKG_VERSION:=1.0
     7  PKG_RELEASE:=1
     8  PKG_MD5SUM:=4584f226523776a3cdd2fb6f8212ba8d
     9 
    10  PKG_SOURCE_URL:=http://www.foosoftware.org/downloads
    11  PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
    12 	PKG_CAT:=zcat
    13	
    14	PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
    15	PKG_INSTALL_DIR:=$(PKG_BUILD_DIR)/ipkg-install
    16
    17	include $(TOPDIR)/package/rules.mk
    18
    19	$(eval $(call PKG_template,FOO,foo,$(PKG_VERSION)-$(PKG_RELEASE),$(ARCH)))
    20
    21  $(PKG_BUILD_DIR)/.configured: $(PKG_BUILD_DIR)/.prepared
    22          (cd $(PKG_BUILD_DIR); \
    23                  $(TARGET_CONFIGURE_OPTS) \
    24                  CFLAGS="$(TARGET_CFLAGS)" \
    25                  ./configure \
    26                  --target=$(GNU_TARGET_NAME) \
    27                  --host=$(GNU_TARGET_NAME) \
    28                  --build=$(GNU_HOST_NAME) \
    29                  --prefix=/usr \
    30                  --sysconfdir=/etc \
    31 			--with-bar="$(STAGING_DIR)/usr" \
    32          );
    33          touch $@
    34
    35  $(PKG_BUILD_DIR)/.built:
    36      	rm -rf $(PKG_INSTALL_DIR)
    37		mkdir -p $(PKG_INSTALL_DIR)
    38		$(MAKE) -C $(PKG_BUILD_DIR) \
    39 	          $(TARGET_CONFIGURE_OPTS) \
    40            install_prefix="$(PKG_INSTALL_DIR)" \
    41 	          all install
    42		touch $@
    43 
    44  $(IPKG_FOO):
    46		install -d -m0755 $(IDIR_FOO)/usr/sbin
    47    	cp -fpR $(PKG_INSTALL_DIR)/usr/sbin/foo $(IDIR_FOO)/usr/sbin
    49		$(RSTRIP) $(IDIR_FOO)
    50		$(IPKG_BUILD) $(IDIR_FOO) $(PACKAGE_DIR)
    51	
    52	mostlyclean:
    53  	make -C $(PKG_BUILD_DIR) clean
    54    	rm $(PKG_BUILD_DIR)/.built
</pre>

    <p>First of all, this <i>Makefile</i> example works for a single
    binary software. For other software such as libraries or more
    complex stuff with multiple binaries, it should be adapted. Look at
    the other <code>Makefile</code> files in the <code>package/</code>
    directory.</p>

    <p>At lines 5-15, a couple of useful variables are defined:</p>

    <ul>
     <li><code>PKG_NAME</code> : The package name, e.g. <i>foo</i>.</li>
     
     <li><code>PKG_VERSION</code> : The version of the package that
     should be downloaded.</li>

     <li><code>PKG_RELEASE</code> : The release number that will be
     appended to the version number of your <i>ipkg</i> package.</li>

     <li><code>PKG_MD5SUM</code> : The md5sum of the software archive.</li>

     <li><code>PKG_SOURCE_URL</code> : Space separated list of the HTTP
     or FTP sites from which the archive is downloaded. It must include the complete
     path to the directory where <code>FOO_SOURCE</code> can be
     found.</li>

     <li><code>PKG_SOURCE</code> : The name of the tarball of
     your package on the download website of FTP site. As you can see
     <code>PKG_NAME</code> and <code>PKG_VERSION</code> are used.</li>

     <li><code>PKG_CAT</code> : The tool needed for extraction of the 
	software archive.</li>

     <li><code>PKG_BUILD_DIR</code> : The directory into which the software
     will be configured and compiled. Basically, it's a subdirectory
     of <code>BUILD_DIR</code> which is created upon extraction of
     the tarball.</li>

     <li><code>PKG_INSTALL_DIR</code> : The directory into the software 
     will be installed. It is a subdirectory of <code>PKG_BUILD_DIR</code>.</li>

    </ul>

    <p>In Line 3 and 17 we include common variables and routines to simplify
	the process of ipkg creation. It includes routines to download, verify
	 and extract the software package archives.</p>

    <p>Line 19 contains the magic line which automatically creates the 
	ipkg for us.</p>

    <p>Lines 21-33 defines a target and associated rules that
    configures the software. It depends on the previous target (the
    hidden <code>.prepared</code> file) so that we are sure the software has
    been uncompressed. In order to configure it, it basically runs the
    well-known <code>./configure</code>script. As we may be doing
    cross-compilation, <code>target</code>, <code>host</code> and
    <code>build</code> arguments are given. The prefix is also set to
    <code>/usr</code>, not because the software will be installed in
    <code>/usr</code> on your host system, but in the target
    filesystem. Finally it creates a <code>.configured</code> file to
    mark the software as configured.</p>

    <p>Lines 35-42 defines a target and a rule that compiles the
    software. This target will create the binary file in the
    compilation directory, and depends on the software being already
    configured (hence the reference to the <code>.configured</code>
    file). Afterwards it installs the resulting binary into the 
    <code>PKG_INSTALL_DIR</code>. It basically runs 
    <code>make install</code> inside the source directory.</p>

    <p>Lines 44-50 defines a target and associated rules that create
    the <i>ipkg</i> package, which can optionally be embedded into
    the resulting firmware image. It manually installs all files you
    want to integrate in your resulting ipkg. <code>RSTRIP</code> will
    recursevily strip all binaries and libraries. 
    Finally <code>IPKG_BUILD</code> is called to create the package.</p>

    <h3>Conclusion</h3>

    <p>As you can see, adding a software to buildroot is simply a
    matter of writing a <i>Makefile</i> using an already existing
    example and to modify it according to the compilation process of
    the software.</p>

    <p>If you package software that might be useful for other persons,
    don't forget to send a patch to OpenWrt developers! 
    Use the mail address: openwrt-devel@openwrt.org   
    </p>

     <h2><a name="links" id="links"></a>Resources</h2>

    <p>To learn more about OpenWrt you can visit this website: 
     <a href="http://openwrt.org/">http://openwrt.org/</a></p>

  </div>

  <div class="main">
    <div class="titre">
      <h1>OpenWrt Kernel Module Creation Howto</h1>
    </div>

    <h2><a name="about_module" id="about_module"></a>About OpenWrt Kernel Module Compilation</h2>

	<p>You are planning to compile a kernel module? This howto will
explain what you have to do, to have your kernel module installable as
an ipkg.</p>

    <h2><a name="kernel" id="kernel"></a>Enable the kernel options</h2>

	<p>Enable the kernel options you want by modifying
build_mipsel/linux/.config. We are assuming, that you already had your
kernel compiled once here. You can do the modification by hand or by 

<pre>
$ cd build_mipsel/linux
$ make menuconfig
</pre>

And copy it, so your changes are not getting lost, when doing a 'make
dirclean'. Here we assume that you are compiling for Broadcom chipset
based devices:

<pre> $ cp .config ../../../target/linux/linux-2.4/config/brcm </pre>

</p>
    <h2><a name="buildroot_option" id="buildroot_option"></a>Create a buildroot option</h2>

	<p>Create a buildroot option by modifying/inserting into
target/linux/Config.in, e.g.

<pre>
config BR2_PACKAGE_KMOD_USB_KEYBOARD
        tristate "Support for USB keyboards"
        default m
        depends BR2_PACKAGE_KMOD_USB_CONTROLLER
</pre>
</p>

    <h2><a name="binary" id="binary"></a>Define the binary files for the kernel module</h2>

	<p>Define the binary files for the kernel module by modifying/inserting into
target/linux/linux-2.4/Makefile, e.g.

<pre>
$(eval $(call KMOD_template,USB_KEYBOARD,usb-kbd,\
	$(MODULES_DIR)/kernel/drivers/input/input.o \
	$(MODULES_DIR)/kernel/drivers/input/keybdev.o \
	$(MODULES_DIR)/kernel/drivers/usb/usbkbd.o \
,CONFIG_USB_KEYB,kmod-usb-core,60,input keybdev usbkbd))
</pre>

Where CONFIG_USB_KEYB is the kernel option, USB_KEYBOARD is the last
part of BR2_PACKAGE_KMOD_USB_KEYBOARD and usb-kbd is part of the
filename of the created ipkg.</p>

    <h2><a name="control" id="control"></a>Specify the ipkg control file</h2>

	<p>Create e.g. target/linux/control/kmod-usb-kbd.control with content similar to this:

<pre>
Package: kmod-usb-kbd
Priority: optional
Section: sys
Maintainer: Markus Becker &lt;mab@comnets.uni-bremen.de&gt;
Source: buildroot internal
Description: Kernel Support for USB Keyboards
</pre>
	</p>

    <h2><a name="compile" id="compile"></a>Compile the kernel module</h2>

	<p>Enable the kernel module with
<pre>
$ make menuconfig
</pre>
	in TOPDIR and selecting it.<br>

	Compile with
<pre>
$ make dirclean && make
</pre>
	</p>
  </div>

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